TLUD help

Hey guys, I was hoping someone might be able to help me solve a little problem.
I built a small TLUD for making biochar out of a 1gal paint can and a small length of pipe as a chimney. I drilled a bunch of holes (about 20) at the bottom of the paint can and cut out a circle in the middle of the lid that's just slightly smaller than the pipe that I used for the chimney so that it can sit on top of it. I just used sticks that I found laying around and small chunks of firewood that I cut to fit inside.
I propped it up on two bricks so there would be airflow to the bottom, then lit it with the top off just to get it going. Then when it was lit well I put on the top (which has the hole in the middle) and it got really smokey. Basically it burned pretty well and with surprisingly little smoke when it was just an open fire. When I put on the top and the chimney, it started smoking a lot. Any idea what I'm doing wrong? I think I should have used better fuel first of all, but I'm thinking maybe I should drill a few holes in the pipe that I'm using as a chimney to get a little more air to it, even though it's supposed to be a low-oxygen burn.

It did make charcoal though, so it wasn't a total loss. I'd just prefer to not make an incredibly smokey fire and waste half of my fuel if at all possible.

You might take a look at this design.

I have made several and have had very good luck. Make sure your fuel is very dry.

http://www.bioenergylists.org/files/1G%20Toucan%20TLUD%20for%20Biochar%20Jan%202010%20-%20final_0(3).pdf

Ken

I didn't see you mention that you put holes in the chimney for secondary air...
You need secondary air into the chimney to re-ignite the smoke.

Kirk Mobert wrote:I didn't see you mention that you put holes in the chimney for secondary air...
You need secondary air into the chimney to re-ignite the smoke.

Ah, this could be the problem. I'll try drilling some.

Thanks!

Start small with the holes..
The size and/or number of them will be pretty important. To burn all of wood gas, you need the right amount of air, not too much, not too little.
I'd put a small amount of small holes around the base of the chimney and test it.. If it's not right, bore out the holes a size larger and/or add more.
It will run smoky with too little air AND with too much, so you'll want to move in small increments and test fire it a lot.
When it burns clean, there you are.